Synthesis and self‐assembly of poly(styrene)‐b‐poly(N‐vinylpyrrolidone) amphiphilic diblock copolymers made via a combined ATRP and MADIX approach

Abstract

Amphiphilic diblock copolymers of polystyrene (PS) and poly(N-vinylpyrrolidone) (PNVP) were prepared by a combination of ATRP and MADIX. Well-defined PS with bromine end group was synthesized by ATRP in bulk at 110 8C using (1-bromoethyl) benzene as an initiator. The Br-end group was then converted to xanthate as verified by 1 H NMR spectroscopy, elemental analysis, and UV-spectroscopy. PS-b-PNVP copolymers were produced by MADIX of NVP in bulk at 60 8C using PS-xanthate as a macro-chain transfer agent and the kinetics of polymerization were investigated. The structures of PS-b-PNVP were characterized using GPC and 1 H NMR. Amphiphilic PS-b-PNVP could form spherical micelles with PS cores and PNVP shells in aqueous solution as confirmed by 1 H NMR and laser light scattering (LLS). The values of critical micelle concentration of PS-b-PNVP and the average aggregation number of PS-b-PNVP in the micelles were measured using pyrene as a probe and static LLS, respectively. The aggregation number increases concomitantly with temperature (10-50 8C), but the hydrodynamic radius of the micelles remains almost constant over the same temperature range, which may indicate shell dehydration at a higher temperature. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: [5604][5605][5606][5607][5608][5609][5610][5611][5612][5613][5614][5615] 2008

Living Radical Polymerization by the RAFT Process - A Second Update

“…Several groups [495,496] have reported processes where a first block comprising a 'more activated monomer' is prepared by ATRP and then a second block comprising a 'less activated monomer' is prepared by RAFT (e.g., PtBA-b-PVAc, Scheme 21 [495] or PStb-PNVP [496] ). Sequential ATRP and RAFT has also been used to prepare block copolymer brushes.…”

Synthesis and applications of polystyrene-block-poly(N-vinyl-2-pyrrolidone) copolymers

“…Hussain et al [20] produced amphiphilic PS-b-PVP copolymer starting from PS obtained by ATRP followed by RAFT of PVP. The authors used acetone as the solvent for conversion of the ATRP product (PS-Br) into RAFT macro-CTA, however acetone is not a solvent for this homopolymer [31] .…”

“…Macro-CTA was prepared by ionic substitution reaction, similar to a previously reported procedure [20,27] . In a two neck round bottom flask, potassium ethyl xanthogenate (0.267 g, 1.66 mmol) was dissolved in acetone (6.00 mL).…”

“…Amphiphilic copolymers of polystyrene-block-poly(N-vinyl-2-pyrrolidone) (PS-b-PVP) have been reported employing the following radical polymerizations: pseudo-living [18] , atom transfer radical polymerization (ATRP) [9,19] , ATRP followed by reversible addition−fragmentation chain-transfer polymerization (RAFT) [20] , RAFT [21] , RAFT followed by ATRP [22] , nitroxide-mediated polymerization (NMP) [23,24] , organostibine-mediated [25] and organogermanium-mediated polymerizations [26] . Although PS-b-PVP copolymers have been synthesized by several methods, some did not provide suitable PS-b-PVP amphiphilic copolymers due to the presence of homopolymers as impurities and high Ɖ values (i.e.…”

“…For this reason, styrene was initially synthesized in bulk by ATRP leading to polystyrene with bromine chain end functionality. Then, a suitable macro chain transfer agent (macro-CTA) was formed by performing a simple method [20,27] to convert the polystyrene ATRP product into the RAFT agent. N-vinyl-2-pyrrolidone (VP) was subsequently used as a chain extensor of this RAFT agent to synthesize well-defined amphiphilic PS-b-PVP copolymers.…”